Images of secondary ion distributions of RB-QD04-0047-02 by ToF-SIMS before pre-sputtering. Images of secondary positive (+) and negative (−) ion distributions of RB-QD04-0047-02 by ToF-SIMS (before pre-sputtering) with its backscattered electron image by SEM. The brighter color corresponds to higher concentrations of secondary total ion and specific ion (m/z). Note that intense ions were emitted more from the background rather than the particle itself. Scale bars of ToF-SIMS analysis are 10 μm.